1. Field of Invention
The invention relates to a remote control system for on-vehicle equipment and a remote control method. More specifically, this invention relates to a remote control system for on-vehicle equipment that includes a portable unit and an on-vehicle unit that executes a predetermined process when a code content of a response signal issued by the portable unit in response to a transmitted request signal matches a required code content, and a remote control method for the same.
2. Description of Related Art
An on-vehicle equipment remote control system provided with a portable unit and an on-vehicle unit, which controls permission or non-permission of use of a vehicle based on the result of a code collation of a communication between the two units, has been known. An example of this kind of system is disclosed in Japanese Laid-Open Publication No. 2000-103316. This system, when a code content of a response signal issued by the portable unit in response to a code request signal from the on-vehicle unit matches a required code content, permits the locking or unlocking of a vehicle door, or permits the start of an internal combustion engine that powers a vehicle. Therefore, this system enables locking or unlocking of a vehicle door remotely and without contact, using the communication between the on-vehicle unit and the portable unit. This system also enables a vehicle operator to cause the internal combustion engine to start without inserting an ignition key into a key cylinder.
If the internal combustion engine is started in this way without inserting the ignition key into the cylinder, however, there is the possibility that the portable unit may be taken away from the vehicle while the internal combustion engine is operating. If the portable unit is taken away from the vehicle and the vehicle continues operating in that state, a problem is caused whereby locking or unlocking of the door or re-starting the internal combustion engine will become impossible once the internal combustion engine has then stopped operating.
Therefore, this system verifies whether the portable unit is present inside the vehicle using the communication between the on-vehicle unit and the portable unit when the vehicle is in a used state due to the operating of the internal combustion engine. As a result of this verification, if the portable unit is determined not to be present inside the vehicle, an alarm is issued to the vehicle operator. Therefore according to this system, it is possible to prevent the taking away from the vehicle of the portable unit which is necessary for controlling permission or non-permission of vehicle use, and which the vehicle operator needs to carry.
The higher a frequency of a radio wave is, in other words, the shorter the wavelength of the radio wave is, the stronger its directional stability becomes, the weaker its turnaround is, and the easier it is to attenuate it. For this reason, if the communication from the on-vehicle unit to the portable unit (hereinafter referred to as a “downlink communication”) utilizes a high frequency radio wave that has weak turnaround and is easy to attenuate, and if, for example, the system is utilized while the portable unit is inside the pocket or the like of a vehicle operator, since the body of a person or the like becomes interpositioned between the on-vehicle unit and the portable unit, a situation may arise where the radio wave from the on-vehicle unit may not reach the portable unit, despite the portable unit being present in the proximity of the on-vehicle unit. Also, it is necessary to transmit the radio wave with a high electromagnetic strength to ensure a required communication area in this case. However, if the high frequency radio wave is utilized for the downlink communication, a stable communication area between the on-vehicle unit and the portable unit cannot be secured, and a situation arises where highly efficient and secure communication between the two units cannot take place.
This conventional system utilizes a comparatively low frequency LF band (specifically 134 kHz) radio wave for the downlink communication from the on-vehicle unit to the portable unit. Therefore, this system ensures the stable communication area because the portable unit receives the request signal from the on-vehicle unit reliably, even if the body becomes interpositioned between the two units.
When the internal combustion engine that powers the vehicle or an inverter of an electric vehicle or the like is operating, however, broad band noise such as ignition noise, motor noise or inverter noise is generated. The lower a frequency of this kind of noise is, the larger its energy. Therefore, the lower the communication frequency between the on-vehicle unit and the portable unit, the easier it becomes for that radio wave to be superimposed by the noise. Therefore, if, as in this conventional system, the communication between the on-vehicle unit and the portable unit utilizes the comparatively low frequency radio wave such as the LF band even after the start of an internal combustion engine or the like, it becomes easier for communication errors to be generated, due to the noise generated by the operation of the internal combustion engine or the like. If communication errors are generated between the on-vehicle unit and the portable unit, verification of the presence of the portable unit inside the vehicle, that is verification that the portable unit has not been taken away from the vehicle, cannot then be carried out with a good degree of accuracy.